vbox: Don't leak arrays from XPCOM

XPCOM returns an array as a pointer to an array of pointers to the
actual items. When the array isn't needed anymore the items are
released, but the actual array containing the pointers to the items
was not freed and leaked.

Free the actual array using ComUnallocMem.

This doesn't affect MSCOM as SafeArrayDestroy releases all items
and frees the array.

src/vbox/vbox_XPCOMCGlue.c

@@ -339,6 +339,8 @@ vboxArrayRelease(vboxArray *array)
         }
     }
 
+    pVBoxFuncs_v2_2->pfnComUnallocMem(array->items);
+
     array->items = NULL;
     array->count = 0;
 }
@@ -365,6 +367,8 @@ vboxArrayUnalloc(vboxArray *array)
         }
     }
 
+    pVBoxFuncs_v2_2->pfnComUnallocMem(array->items);
+
     array->items = NULL;
     array->count = 0;
 }